Leak detector



P 1, 1952 w. c. WHITE 7 2,591,485

' LEAK DETECTOR Filed April 26, 1950 Inventor 1 William C'.White,

His Attorney.

above- Patented Apr. 1; 1952 UNITED PATENT OFFICE 2,591,485 LEAK nETEoToR Willlain'C. White, Schenectady, N. Y., assignor'to General Electiicflompany, a. corporation of New York ahfiiihhhth hp'rii "2t, 1950, Serial No. 158,269

This ihveh'tioh relates "to improvements in the method and apparatus for detecting cei t'aih s u'bstances present in gases aha whereas 'des'cribed in cope'hiiin'g abplica'tioh serial No. 754,657, filed June 14, 1947, by Chester W. -Ri'ce 'a'iid assigned to the same jassig'n'ee as the present ihileh'tion, which is nowPa't'eht No. 25550;498.

In the 'ab ove-citeiii "aiiiplieatibn there are described methods arid apparatus for ifiti'oducifig certain substances such asv'a-boi s, smokeshr other particles of matterand *g asesih an atmosphere, Which'ihfair be sushet'tea of 'coiita'ining fa concentiation 6f 'the substances to 'be *d acted, into an electrical dischai ge device under c'ohai'tions which bei mit the Sub's'taLh'de iiiitll'itx positive i011 frotmstioh at there "positively charged heatefq electrode, the 'p bsiti'v'e ions so formed being ii'ollected by a negatively eha'rgd electrode 15Clp'roduc'e an ihdic'atin'g currerittvhich iiicreas'es with the cohcentr'ationofthe substance. bevicesot thistype have been "foiind to be qu'ali'tative'ly elective to various substances, that is, they respond only to certain types of substances such as the "alltali metals, or other substances having ionization potential less than the eleotzdh work fiihcfioh (if the electrodes therein, thehawgeh -elements,pr compounds of either. For shbsth cess chas the alkali metals ain tithei'r communes-such ioh formation apparently occurs by "i'oiiiZ tion bf the substance itself Wh'eh it cbfh'e s irito *eontac't with the heated electrode. halogens "afld their -c61m)'(fiifids, the sthstahee appe'arsto tiau'se 'idn 'fb'i'matiohohljfi'h th'eiirsence of "w11at inightb'e called sens'i'iii'z' g cohibouhds such 'tliealkaliinetals or'their it appears 'in this ease "that "the s iifig inaterials tli'e'mseivs armament temzea a flcifii the cles'iied positive ioh ciiirefit.

The heha fse'c'tion contains a gas inlet Search tiibeft-he' sehs'i'tii e elehierit'itself, a blower 01f "pump tos'i'ltik Tn thegas to be tested and "an ifhaiist i'idlt. ijsitivo ion currentactuates a meter or other d don'- tamed in the 'chtSSis also 'coritsihs the hower sup ry'rqr apart at the circuit.

The divisionof'the detectorfapparatu's into head and chassis sectionswas adbpted"forvei-y definite reasons. Ineiiibaraitusof the 'pi'esntty pe, it is imperative that it be 'fiib" ed and ai iblied inv'arious positions and locationsaiidbe eitreihelysensi ti-ve to the "presence of the "substances "to -be he- For ethers, such as the teted and also that the response toth'eii' presence beveryrapid. 'It's recovery to a sensitive condition after'havingdetected the coht'amihaht should also be rapid. Ai'i inherent characteristic of the device is that its sensitivity and the time "of respoiise decreases as the rate of flow of gas or vapor containing the substance to be detected through the sensitive element increases probably due to the factthat only a smaller proportion of the foreign substance has "a siifiicient time to contact the anode and thus form positive ions. While it "has been "suggested th'atthe blower or pump, as well as the discharge 'tiibe, be located in the chassis and gas "draw the' eto through "a long tubingwhich wofild greatly reduce th'evfeig ht of or ess'entiallyelinii-hate th'e head as 'no'w 'kho'w il, the seemingly impossible compromise between sensitivity and the time delay of response to a substance has'prevented'suoha simplification of the apparatus. As pointed out above, to draw a gas at a high rateoffiow'through the tubi'ngfinto and through the sensitive element in order to obtain a'quick 'respon'seto leaks and the like as the outerend 'o'f'the tubing is passed over a surface, causes the element to be less '"s'ehsitive due toth'e lesser contact of the gasor substance with the positively charged electrode *"or anode.

As a result of the "above compromise between sensitivity andtim'e of ie'spo'nse when the sensitive element is located in the 'chassis and the gas or substance to bedetect'edi's drawniiito 'theiiischarge tube through a search tube, itis customary to mount thesensitive elemeht' aiid'suctionbloit'er or pump in a headiinitahd'th'e iniiicating'me'ans and other equipment in a chassis unit. only by this means has it been possible to obt'aiinthe desired 'quickres'p'onse o'r generation of positive ion current "which is transmitted to the in'dicating element inthe chass'is.

'While'the Weight of thehead unit is reduced as inu'ch as DOS SibIB, it is still heavy and awkward eriough 't'o 'c'letr'act'fio'ni easy manipulatibn for the dtetion "(if leaks; in venous equipment on a produe'ti'o'n basis "where 'each location must be searched d1 examines With the 'he'adin a minimum of time. Also, it is desirable that the relatively fragilesensitive element or tube "be remote from a head which is subject to jars and shocks.

Another object of the present invention is to provide apparatus of the above type in which the discharge element and pump or blower are located in the chassis instead of in a separate head.

A further object of the invention is to provide apparatus of the above type having the detector equipment in a chassis, with samples drawn through a tubing, which has a high sensitivity and-a fast response to the material being tested.

Other objects will become apparent and the invention better understood from a consideration of the following description and the drawing in which the single figure shows a typical embodiment of the present invention.

It has been found that the above objects may be realized very simply.

More particularly, it has been found that apparatus of the above type having the discharge element and blower in the chassis, and having good sensitivity and a fast response time to detectable substances, may be made by using relatively fine tubing or conduit to draw the sample into the space between discharge elements, which has a substantially greater cross section.

.In the drawing, the discharge device I coinprises an envelope 2, a positively charged electrode 3 which is heated by filament 4 and a negative electrode 5. The gas or vapor to be tested enters the envelope 2 through inlet conduit 6 mounted in insulating bafile l6 and exhausts through outlet conduit 1. The heating filament 4 may be energized by any suitable means such as by the secondary 8 of transformer 9 which is energized by power impressed in turn upon its primary coil It]. Any suitable source may be used to establish a potential difference between electrodes 3 and such as battery II. A microammeter I2 or other current indicating device is connected in series with the electrodes and battery II as shown to detect and signal changes in the positive ion current flowing between the electrodes.

In order to provide a desired flow of air or gas through the discharge tube I, pump I3 is provided in conduit I4 leading from the exhaust port I of the discharger. Pump I3 may be mechanical or of the water aspirator variety or of other types, it being preferred that it create a vacuum up to twenty-five inches of water for some applications. The inlet tubing or conduit is shown at I5 and may be arranged readily to connect with conduit 6.

As pointed out above, it is desirable in this type of apparatus that any impurity in a gas or vapor which it is desired to detect cause a quick change in the positive ion current flowing between electrodes 3 and 5 to indicate the presence of the substance. It is also necessary that the fiow of the gas or vapor through the discharge tube not be too fast lest the substance being carried in the gas or vapor not have sufficient time to contact positive electrode 3 to produce enough positive ions to give sufiicient indication of its presence. Too fast a passage of the gas through discharger I thus reduces the sensitivity of the device.

It is likewise apparent that if the search tube I5 has about the same cross-section, say that of a five thirty-second inch inside diameter tube in the proposed apparatus, as when the detecting means is immediately adjacent or close to the gas inlet in the separate head, it would take a relatively long time for the sample of gas to be tested to reach the discharge tube I.

If the size or inside diameter of the inlet tube or search tube l5 be small and sufficient suction applied the gas to be detected travels through it at a high rate of speed. Furthermore, since the cross-section area of tubing I5 and inlet conduit 6 are' substantially smaller than the annular space between the electrodes of the sensitive element, the gas, once inside the element, expands and slows down so as to give the substance contained therein an ample opportunity to contact and quickly produce indicating positive ions at electrode 3. For example, using a search tubing about one-twentieth of an inch in inside diameter and about eight feet long, an indication was given on microammeter I2 of the presence of a detectable substance in an entrant gas after a delay of only about one second. By adjusting the amount of vacuum produced by pump l3, the length of the tubing I5 may be varied, it being kept in mind that conditions should not be so adjusted as to produce too fast a fiow through the sensitive element with a resultant loss in sensitivity.

It is necessary that tubing 15 be fabricated of material which will not give off a halogen compound vapor or react with the gases or vapors to be detected. Polyethylene tubing has been found to be resistant to many substances. Polytetrafluoroethylene is another suitable tubing material which is quite inert. Others will occur to those skilled in the art. I

By this invention there is provided a quick response device for detecting substances in gas and vapors where the detecting apparatus is all 10- cated in a singlecompact unit which may be kept in a favorable stationary position while the gas or vapor to be detected-is sampled through a conveniently held, easily movable and flexible tubing. Whereas formerly a heavy and bulky search head had to be held to the gas source to be tested, now the gas maybe sampled by merely holding the end of a long small diameter flexible tube to the source. I

The invention is of further advantage in that using thesmall inlet tube as described herein, the introductionof dust particles which ma short circuit the element is minimized. Furthermore, the tube may be easily removed for cleaning and may be made of varying lengths to suit the requirements of any particular job.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. Apparatus for detecting a foreign substance in an atmosphere comprising an electric discharge device including a pair of electrodes, means for imposing an electrical potential dif ference between saidelectrodes, means for heating the more positive of said electrodes, means for causing a, controlled flow of the atmosphere between said electrodes, said means comprising a vacuum pump and aconduit'to the space between said electrodes, said conduit having a cross-sectional area substantially smaller than the space between said electrodes, and means for detecting changes in the current between said electrodes caused by the formation of positive ions in said device due to the presence of the substance.

2. Apparatus as in claim 1 in which the substance is of a class having an ionization potential less than the electron work function of the more positive of the electrodes.

3. Apparatus as in claim 1 wherein said sub stance is of the class comprising the alkali metals and compounds thereof.

4. Apparatus as in claim 1 wherein said substance is of the class comprising the halogen elements and compounds thereof.

5. The method of 'operating a detector for foreign atmospheric substance of the type comprising an electrical discharge device including a pair of electrodes, means for imposing an electrical potential between said electrodes, means for heating the more positive of said electrodes, means for detecting changes in the current between s'aid electrodes caused by the formation of positive ions within said device due to the presence of said substance, and means for caus ing a controlled flow of said atmosphere between said electrodes, which method comprises restricting the cross-sectional flow area of gas flowing toward said electrodes while maintaining rela tively unrestricted the cross-sectional flow area of gas flowing past said electrodes.

WILLIAM C. WHITE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

